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Dr S. B. Desai (F) (Department of the Environment, Transport & the Regions)
I congratulate Professor Beeby for drawing the attention of structural engineers to some important problems in the provision of structural safety at a conceptual level. During his presentation, he emphasised that adequate safety factors, adequate robustness, and the avoidance of mistakes, are three independent requirements for the provision of structural safety. However, I am concerned that the following statements in his paper remain open to misinterpretation by engineers: Page 16 (‘Introduction’): ‘Adequate robustness is provided so that the structure can withstand accidents and unforeseen events without suffering damage disproportionate to the cause’. Page 18 (‘Mistakes’): ‘One thing that can be done to limit the consequences of mistakes is to provide “robustness”’
A structure is vulnerable if any damage produces consequences that are disproportionate to that damage; conversely, a structure is robust if it can withstand arbitrary damage. The purpose of this paper is to present a new theory of structural vulnerability. It is a theory of structural form and connectivity, the purpose of which is to identify the ‘weak links’ within a structure. It is not a theory of the response of a structure to loads.
Z. Lu, Y. Yu. N.J. Woodman and Professor D.I. Blockley
Mr E C. Beale, from South Croydon, provides more background to the thinking behind his
contribution to our 16 February 1999 column:
Given that CO, emissions from humans are several times as great as the total from fossil fuels, it would seem that the minimum would be 3 times as great and that livestock emissions might be as great again. This does not take account of all the sources of CO, in the natural world, which might be as great as the previous total.